Piston with sealed cooling gallery containing a thermally conductive composition

Abstract

A heavy duty piston for an internal combustion engine comprises a thermally conductive composition filling 10 to 90 vol. % of a sealed cooling gallery. The thermally conductive composition includes bismuth and/or tin. For example, the thermally conductive composition can be a single-phase binary mixture of bismuth and tin. The thermally conductive composition has improved thermal properties, for example a melting point around 139° C., a thermal conductivity around 22 W/m·K, and a thermal diffusivity around 1.43E-5 m2/s. The thermally conductive composition is not reactive and does not include toxic or cost-prohibitive metals. During high temperature operation, as the piston reciprocates in the cylinder bore, the thermally conductive composition flows throughout the cooling gallery to dissipate heat away from the upper crown and thus improve efficiency of the engine.

What is claimed is: 
     
       1. A piston for an internal combustion engine, comprising:
 a body portion including an upper crown and a cooling gallery extending along least a portion of said upper crown, said cooling gallery being sealed; 
 a thermally conductive composition disposed in said cooling gallery; and 
 said thermally conductive composition consisting of bismuth in an amount of 57 wt. % and tin in an amount of 43 wt. %, based on the total weight of said thermally conductive composition. 
 
     
     
       2. The piston of  claim 1 , wherein said thermally conductive composition has a melting point of 139 to 250° C., a thermal conductivity of 16 to 31 W/m·K, and a thermal diffusivity of 1.13 E-5 m 2 /s to 1.86 E-5 m 2 /s. 
     
     
       3. The piston of  claim 1 , wherein said thermally conductive composition consists of a single-phase and is unreactive. 
     
     
       4. The piston of  claim 1 , wherein said thermally conductive composition has a melting point of 139° C.; said thermally conductive composition has a thermal conductivity of 22 W/m·K; and said thermally conductive composition has a thermal diffusivity of 1.43E-5 m 2 /s. 
     
     
       5. The piston of  claim 1 , wherein said thermally conductive composition fills 10 to 90 vol. % of said sealed cooling gallery, based on the total volume of said cooling gallery. 
     
     
       6. The piston of  claim 1 , wherein said body portion is formed of a steel material;
 said body portion extends circumferentially around a center axis and longitudinally along said center axis from an upper end to a lower end; 
 said upper crown presents an outer surface and an oppositely facing inner surface and said cooling gallery extends along least a portion of said inner surface of said upper crown; 
 said outer surface of said upper crown presents a bowl-shaped configuration at said upper end; 
 said upper crown includes a first outer rib and a first inner rib each extending circumferentially around said center axis and longitudinally from said upper end toward said lower end, said first inner rib is disposed between said first outer rib and said center axis; 
 said outer surface of said first outer rib presents a plurality of ring grooves facing away from said center axis and extending circumferentially around said center axis for holding piston rings; 
 said body portion includes a lower crown extending from said upper crown to said lower end; 
 said lower crown presents an outer surface and an oppositely facing inner surface, and said cooling gallery extends along least a portion of said inner surface of said lower crown; 
 said lower crown includes a second outer rib connected to said first outer rib and a second inner rib connected to said first inner rib, said second ribs extends circumferentially around said center axis between said upper end and said lower end to form said sealed cooling gallery between said inner ribs and said outer ribs along a portion of said inner surface of said upper crown; 
 said second ribs are connected to said first ribs by welds; 
 said outer surface of said lower crown presents at least one ring groove; 
 at least one of said upper crown and said lower crown includes an opening extending into said cooling gallery for allowing said thermally conductive composition to be fed into said cooling gallery; 
 said inner surface of said upper crown and said inner ribs present a cooling chamber therebetween, said cooling chamber extends radially along a portion of said inner surface of said upper crown and longitudinally along said center axis and is open towards said lower end for being exposed to a cylinder bore; 
 said body portion includes a pair of pin bosses depending from said lower crown, said pin bosses including a pair of laterally spaced pin bores extending perpendicular to said center axis; 
 said body portion includes a skirt depending from said lower crown, said skirt being joined laterally to said pin bosses and spacing said pin bosses from one another; 
 said skirt includes an outer surface being convex for cooperation with said cylinder bore; 
 said thermally conductive composition fills 10 to 90 vol. % of said sealed cooling gallery, based on the total volume of said cooling gallery; 
 said thermally conductive composition consists of said bismuth and tin; 
 said thermally conductive composition is a medium, and the medium is a metallic composition; 
 said thermally conductive composition has a melting point of 139 to 250° C.; 
 said thermally conductive composition consists of a single-phase and is unreactive; 
 said thermally conductive composition has a thermal conductivity of 16 to 31 W/m·K; 
 said thermally conductive composition has a thermal diffusivity of 1.13 E-5 m 2 /s to 1.86 E-5 m 2 /s; and 
 further comprising a plug threaded into said opening and sealing said cooling gallery. 
 
     
     
       7. The piston of  claim 6 , wherein said thermally conductive composition has a melting point of 139° C.; said thermally conductive composition has a thermal conductivity of 22 W/m·K; and said thermally conductive composition has a thermal diffusivity of 1.43E-5 m 2 /s.